Optimum Dietary Protein Level Research Articles

An approach to optimizing dietary protein to growth and body composition in walking catfish, Clarias batrachus (Linneaeus, 1758).

Clarias batrachus is a commercially important food fish. In the present study, effect of varying dietary protein levels was evaluated on the survival, growth parameters and proximate composition of C. batrachus. Diets comprising 25%, 30%, 35%, 40%, 45%, and 50% crude protein (CP) were supplied to fish in T1, T2, T3, T4, T5, and T6, respectively, at the rate of 5% of fish body weight for the entire 90 days, twice daily. Size of each stocked C. batrachus was recorded after 15 days. Results revealed 100% survival rate of C. batrachus in all treatments. Significantly highest (P<0.001) mean value of weight gain (g/fish), percent weight gain, daily growth rate, specific growth rate and protein efficiency ratio (PER) in C. batrachus were recorded, reared in T4 by feeding 40% CP in diet. The best FCR value (1.90±0.02) for C. batrachus was obtained in T4 by feeding 40%CP in diet. Mean value of water, ash, fat and protein contents (wet mass) were ranged 74.10-79.23%, 3.12-4.68%, 3.90-4.43% and 13.09-16.79% for C. batrachus in the studied treatment groups. Water content (%) was found significantly (P<0.05) higher in the body of C. batrachus for T1, T2, T3 and T6 than for T4 and T5. Ash was found significantly (P<0.05) higher in the fish reared in T4 and T5. Fat content in the wet body mass of C. batrachus was found significantly higher in T4 and T1. While, significant higher (P<0.05) values of mean protein content was noted in C. batrachus reared in T4 and T5. Body composition of C. batrachus was also categorically affected by body size, however, condition factor showed non-significant correlation in most of the relationships in the present study. Overall, results indicated that feeding appropriate diet (containing 40% CP) to the fish resulted good growth performance, lower FCR and higher protein content in the fish. Present study provides valuable knowledge of optimal dietary protein level in C. batrachus which will help in commercial success of aquaculture.

Optimal dietary protein level for the growth and metamorphosis of bullfrog (Lithobates catesbeianus) tadpoles

This study investigated the effects of dietary protein levels on growth performance, antioxidant capacity, digestive enzyme activity, and metamorphosis rate of the bullfrog (Lithobates catesbeianus) tadpoles. Seven isolipidic and isoenergetic diets were formulated with 24.61%, 28.49%, 33.74%, 37.50%, 44.06%, 48.39% and 53.92% crude protein. Triplicate replicates of tadpoles (growth stage 25 and 0.009 g) were fed with experimental diets two times daily for 11 weeks, and the daily feeding amount was 6.50% of the tadpole's body weight. Weight gain (WG), specific growth rate (SGR), the total antioxidant capacity (T-AOC) and catalase (CAT) activity in the liver, the intestinal trypsin activity (TPS) and metamorphosis rate at stage 42 of bullfrog tadpoles all increased with increasing dietary protein level from 24.61% to 44.06% and then decreased. Based on the second-order polynomial regression analysis of the weight gain and metamorphosis rate at stage 41 vs. dietary protein level, the optimal dietary protein level for bullfrog tadpoles was 42.49% and 46.50%, respectively. In conclusion, the optimum dietary protein level of bullfrog tadpoles was estimated to be 42.49%–46.50% of the diet.

Reassessment of dietary protein and lipid requirements for large yellow croaker, Larimichthys crocea, reared in net pens

AbstractAt present, large yellow croaker, Larimichthys crocea, a carnivorous fish ranked fifth in aquaculture production among marine finfishes in the world, still relies on raw fish diet because formulated feed alone is not able to sustain rapid growth of the fish. The present study evaluated growth, feed utilization efficiency, body composition and antioxidant capacity of large yellow croaker fed diets containing four protein (430, 460, 490 and 520 g/kg) and three lipid (60, 90 and 120 g/kg) levels. Fish weighing 11.4 ± 2.8 g were fed with the test diets in net pens for 8 weeks. Final body weight and nitrogen retention efficiency (NRE) were dependent on dietary protein and lipid levels and their interaction. Weight gain, body protein content, serum catalase (CAT) activity and liver glutathione peroxidase (GSH‐Px) activity were dependent on dietary protein and lipid levels. Phosphorus retention efficiency was dependent on dietary protein level and interaction between protein and lipid levels. Hepatosomatic index, body lipid and energy contents, activities of superoxide dismutase (SOD) and GSH‐Px in serum, and CAT activity and malondialdehyde content in liver were dependent on dietary lipid level. The final body weight and weight gain of fish fed at 490 g/kg protein level did not significantly differ from those fed at 520 g/kg protein level. The final body weight, weight gain and NRE of fish fed at 90 g/kg lipid level were higher than those fed at 60 g/kg lipid level, but did not significantly differ from those fed at 120 g/kg lipid level. The maximum weight gain occurred in fish fed the diets either containing 520 g/kg protein or 90 g/kg lipid. The body lipid content, as well as SOD and GSH‐Px activities in serum, were higher in fish fed the diets with 90 and 120 g/kg lipid compared to fish fed the diets with 60 g/kg lipid. The present study reveals that the optimal dietary protein and lipid levels for large yellow croaker reared in net pens were 490–520 g/kg and 90 g/kg, respectively.

Optimal dietary energy and protein levels for breeding pigeons in the winter "2 + 3" lactation pattern

The nutritional requirements of breeding pigeons depend on their physiological period, breeding pattern, and environmental conditions. Despite works on reduced litter size in winter production to combat high mortality and the poor welfare of squabs, there are few studies on the related nutritional requirements of these pigeons. A total of 432 pairs of European Mimas pigeons were randomly divided into 9 groups in which 3 crude protein (CP) levels (15, 16.5, and 18%) and 3 metabolizable energy (ME) levels (12.2 MJ/kg, 12.4 MJ/kg, and 12.6 MJ/kg) were tested to determine the optimal energy and protein requirements of breeding pigeons in the winter "2+3" breeding pattern. The results showed that ME and CP levels had little effect on the body weight, feed intake, and egg quality of breeding pigeons during the lactation period. An 18% CP diet significantly increased the laying rate and hatchability (P < 0.05), but there was no difference in the laying rate with 18% CP and 16.5% CP during the whole reproductive cycle (P > 0.05). There was a significant interaction between ME and CP levels, and the laying interval of breeding pigeons in group 9 (18% CP; 12.6 MJ/kg) was significantly shortened (P < 0.05). For squabs, the ME level had no effect on growth performance, slaughter performance, or meat quality. The body weight of 21-day-old squabs in the 18% CP group increased by 3.16% compared with that of the 15% CP group, but there was no difference between the 18% CP and 16.5% CP groups. Compared with other experimental groups, group 7 (18% CP; 12.2 MJ/kg) had the fastest growth rate in squabs (P < 0.05), and the corresponding slaughter weight was also the heaviest (P < 0.05). We further found that the height of the squab intestinal epithelium was significantly increased in both the 16.5% CP and 18% CP groups of squabs (P < 0.01), but male breeding pigeons showed a certain degree of oxidative stress with an increase in CP level. In conclusion, the effects of 15 to 18% CP levels and 12.2 to 12.6 MJ/kg ME levels on the reproductive metabolism of breeding pigeons and the growth and development of squabs in the "2+3" breeding pattern during winter are small. For economic efficiency, we suggest that the CP level can be reduced to 16.5% while the ME level should not be less than 12.2 MJ/kg in practical production.

Evaluation of optimal dietary protein levels and meat quality of adult hybrid abalone (Haliotis discus hannai♀ × H. fulgens♂) under two representative water temperatures

In this study, the optimal dietary protein levels for adult hybrid abalone (H. discus hannai♀ × H. fulgens♂) were evaluated at two representative temperatures, and the interactive influences of dietary protein and water temperature on abalone meat quality were examined. Six isoenergetic and isolipidic diets containing graded levels of protein (15%, 20%, 25%, 30%, 35%, and 40%) were fed to the hybrid abalone for 90 days. Based on the specific growth rate, the optimum dietary protein levels for adult hybrid abalone using a quadratic curve model were estimated to be 28.07% and 26.47% of the diet at 23 °C (optimum temperature) and 27 °C (high temperature), respectively. The amount of crude protein in the abalone body increased linearly with the dietary protein levels and water temperature. Antioxidation enzyme activities of abalone muscle, including GPx and GST were significantly affected by the interaction of dietary protein levels and water temperature. As for texture analysis, the abalone kept at 23 °C exhibited higher meat hardness than those fed the same diets at 27 °C. The n-3 PUFAs (particularly DHA and EPA) in abalone meat were significantly influenced by dietary protein levels, and the highest content was observed in the 30% dietary protein group. These levels were not affected by water temperature. In addition, higher dietary protein levels and water temperatures increased the total contents of free amino acids and flavor amino acids (Asp + Glu + Gly + Ala + Arg + Tau). The cooking loss of abalone meat was reduced with increased protein levels and was significantly lower in the 23 °C group, along with a higher meat postmortem pH value. The collagen fiber ratio and collagen content of abalone meat were higher in the 23 °C group. In summary, for multiple diet feeding strategies in practical production of abalone aquaculture, the balance between the seasonally specific feeds cost benefits and the abalone meat quality should be carefully evaluated.

Insulin-like growth factor II, a marker gene for determining the optimum dietary protein level in clownfish Amphiprion ocellaris.

In vivo study was conducted to determine the role of insulin-like growth factors (IGF-II) related to dietary protein utilization. For this early juvenile stage of marine false clownfish Amphiprion ocellaris, 300 numbers of 20-day-old larvae (initial body weight of 18.2±0.027 mg/fish) were used as an experimental animal. Animals were fed for 12 weeks with different dietary protein levels (35, 40, 45, 50, and 55%), using Spirulina maxima as a major protein source. Proximate compositions and amino acid profile of the formulated diet were analyzed by the standard methods. Eventually, significant (P<0.05) mean, body weight gain, absolute growth rate, specific growth rate, and feed conversion ratio were obtained in the fishes fed with 50% of dietary protein, whereas, poor growth performance was noticed in 35% of the dietary protein level fed juveniles. The growth-responsible gene IGF-II expression studies showed the significant upregulation in the growth of the juveniles at 2.05±0.11 for 40%, 3.13±0.20 for 45%, 4.97±0.13 for 50%, and 4.33± 0.24 for 55%, which were higher than the control group 35%. The study concluded that 50% of dietary protein level is optimal for better growth indices in clownfish; A. ocellaris juveniles and IGF-II can be used as a potential marker gene to assess the growth indices in A. ocellaris.

Effects of Different Dietary Protein Levels on the Growth Performance, Physicochemical Indexes, Quality, and Molecular Expression of Yellow River Carp (Cyprinus carpio haematopterus)

A 12-week rearing trial was carried out to estimate effects on the growth performance, physicochemical indexes, quality, and the molecular expression of Yellow River Carp (Cyprinus carpio haematopterus) using five practical diets, including dietary protein levels of 220, 250, 280, 310, and 340 g/kg. The results illustrated that the fish's weight gain (WG) and specific growth rate (SGR) were significantly influenced, with an ascending dietary protein level of up to 250 g/kg (p < 0.05). The carp muscle contents of total saturated fatty acids (∑SFA), monounsaturated fatty acids (∑MUFA), polyunsaturated fatty acids (∑PUFA), and fatty acids (∑FA) decreased significantly with the ascending dietary protein levels, except for the 250 g/kg protein diet (p < 0.05). Only the glutamic acid and total essential amino acid (∑EAA) contents were significantly influenced by the ascending dietary protein levels (p < 0.05). The relative GH expression of the carp muscle significantly decreased with the increase in the dietary protein level up to 310 g/kg, and then it significantly increased (p < 0.05). In the intestines, the peak relative TOR expression was observed on the 220 g/kg protein diet, while the relative 4EBP1 expression was significantly influenced by the dietary protein level up to 250 g/kg (p < 0.05). In the muscle, the peak relative TOR and 4EBP1 expression levels were observed on the 250 g/kg protein diet. In gills, the lowest relative Rhag, Rhbg, and Rhcg1 expression levels were observed on the 250 g/kg protein diet. Based on all of the aforementioned results, the optimal dietary protein level for Cyprinus carpio haematopterus (160.24 ± 15.56 g) is 250-280 g/kg.

Dietary Protein Requirement of Juvenile Dotted Gizzard Shad Konosirus punctatus Based on the Variation of Fish Meal.

An 8-week feeding trial was conducted to investigate the effects of dietary protein levels on growth performance, feed utilization, and energy retention of juvenile dotted gizzard shad Konosirus punctatus based on the variation of fish meal. Fish meal was used as the sole protein source; five semi-purified diets were formulated with varying crude protein (CP) levels of 22.52%, 28.69%, 34.85%, 38.84%, 45.78% (CP1-CP5 diets). A total of 300 uniform juveniles with initial body weight 3.61 ± 0.20 g fish-1 were randomly divided into five groups with three replicates in each group. The results showed that different CP levels did not significantly affect the survival of juvenile K. punctatus (p > 0.05). The values of weight gain (WG) and specific growth ratio (SGR) showed a general enhancing trend and then weakened with increasing dietary CP levels (p > 0.05). Feed utilization also improved with increasing dietary CP levels (p > 0.05), and the optimal feed conversion ratio (FCR) value was found in fish fed the diet with CP3 (p > 0.05). The rise of dietary CP from 22.52% to 45.78% enhanced the daily feed intake (DFI) and protein efficiency ratio (PER) values of K. punctatus (p < 0.05). With the increase of dietary CP levels, daily nitrogen intake (DNI), energy retention (ER), and lipid retention (LR) elevated, while retention (NR), daily energy intake (DEI), and daily lipid intake (DLI) reduced (p < 0.05). No statistical differences in the content of water, crude protein, and crude lipid were observed among different treatments (p > 0.05). The activity of lipase in CP3 and CP4 diets was significantly higher than that of the CP1 diet (p < 0.05). Fish fed CP2 and CP3 diets had significantly higher amylase activity than that of the CP5 diet (p < 0.05). The levels of alanine aminotransferase (GPT) first enhanced and then decreased as dietary CP levels raised. The second-order polynomial regression model analysis of the WG and FCR indicated that the optimal dietary protein level for K. punctatus is about 31.75-33.82% based on the variation of fish meal.

Effects of Varying Quantities of Dietary Protein and Lipid on Growth Performance, Blood Biochemical Parameters, Digestive Histology and Enzyme Activity in Juvenile Gold Fish (Carassius auratus)

Background: Goldfishes are used as an ideal model for nutritional studies in larval and juvenile cyprinids. However, of the limited published data that is available on goldfish, protein requirements have varied from 29% to 53% for goldfish larvae. So the present study was undertaken to determine growth performance of goldfish, C. auratus fed with different dietary protein and lipid levels to develop nutritionally balanced diets. Methods: In this study, Carassius auratus juveniles were fed with six diets containing two protein levels (300 and 400 g/kg) and three lipid levels (40, 80 and 120 g/kg) to evaluate the optimal dietary protein and lipid levels to determine growth performance, blood biochemical parameters, digestive enzyme activity and intestinal and liver histology. Result: According to the findings, gold fish juveniles when fed a casein-dextrin based semi-purified diet containing 400 g/kg dietary protein and 80 g/kg dietary lipid content, maximum development and feed utilisation are seen. Second-order polynomial regression also suggests that a diet with 400 g/kg protein and 80 g/kg lipid is best for juvenile goldfish growth and feed utilisation.

Dietary protein improves flesh quality by enhancing antioxidant ability via the NF-E2-related factor 2/Kelch-like ECH-associated protein 1 signaling pathway in softshell turtle (Pelodiscus sinensis).

An 8-week feeding trial was performed to assess the influence of a gradient of protein levels (14.38-45.23%) on flesh quality, skin color, amino acid profile, collagen, antioxidant capability, and antioxidant-related signaling molecule expression of the softshell turtle (Pelodiscus sinensis). Hardness, gumminess, chewiness, and yellowness values in the plastron and carapace, along with collagen, superoxide dismutase, catalase, total antioxidant capacity, and glutathione peroxidase, all improved with elevating dietary protein up to 26.19%, after which they leveled off. Additionally, total amino acids, flavor amino acids, essential amino acids, and non-essential amino acids in the muscle, as well as the expression of copper/zinc superoxide dismutase, glutathione peroxidase, catalase, manganese superoxide dismutase, NF-E2-related factor 2 were all enhanced by increasing the dietary protein level but not changed by higher protein levels. When dietary protein levels were less than 26.19%, the mRNA expression of Kelch-like ECH-associated protein 1, malondialdehyde, and redness values in the carapace and plastron were reduced, as was the lightness values of the carapace, all of which plateaued at higher protein levels. Using catalase activity and malondialdehyde as the indicators and applying a broken-line analysis, the optimal dietary protein level for P. sinensis was inferred to be 26.07 and 26.06% protein, respectively. In summary, an optimal protein input improved turtle flesh quality by strengthening antioxidant capacity in muscle tissue and by regulating the expression of antioxidant-related enzymes via the Nrf2/keap1 signaling pathway.

Effects of Dietary Cottonseed Protein Concentrate Levels on Growth Performance, Health Status, Flesh Quality and Intestinal Microbiota of Grass Carp (Ctenopharyngodon idellus).

The aim of this study was to evaluate the nutritional value of cottonseed protein concentrate (CPC) as a single dietary protein source and the optimal protein level for grass carp (Ctenopharyngodon idellus). An 8-week feeding trial was conducted by feeding juvenile grass carp (initial body weight: 4.68 ± 0.01 g) with six experimental diets containing graded levels of protein provided by CPC. The results showed that the optimal CPC level (CPC4) improved the growth performance and health status of grass carp. The optimal dietary protein level was estimated to be 38.61 and 38.66% based on specific growth rate (SGR) and feed efficiency (FE), respectively. The CPC4 group significantly increased the total antioxidant capacity (T-AOC) content and glutathione peroxidase (GSH-Px) activity in the hepatopancreas (p &lt; 0.05). In addition, the CPC4 group increased the muscle T-AOC and glutathione (GSH) content and improved muscle hardness, and the gene expression of MRFs, fgf6a, myhc-7, myhc-1, myhc-4, igf-II, and tor was upregulated while mstn gene expression was downregulated (p &lt; 0.05). Correlation analysis revealed that the optimal dietary CPC level promoted grass carp growth, health, and flesh quality by regulating the relative abundance of intestinal microbes. Furthermore, CPC6 upregulated the ko00480 (Glutathione metabolism) and ko00620 (Pyruvate metabolism) pathways compared to CPC1 (p &lt; 0.05), possibly indicating that low dietary CPC levels adversely affected amino acid metabolism in the intestinal microbiota of grass carp, while a high level of CPC will meet the metabolic needs of the body by increasing the utilization of energy.

Evaluation of Optimal Dietary Protein Levels for Juvenile Hybrid Abalone under Three Temperatures: Growth Performance, Body Composition, Biochemical Responses, and Antioxidant Capacity

We studied the effects of dietary protein levels and water temperatures on growth performance, body composition, serum biochemistry, and digestive gland antioxidant enzyme activities of juvenile hybrid abalones Haliotis discus hannai♀ × H. fulgens♂ ( 1.47 ± 0.03 g ; 20.73 ± 0.16 mm ). A 3 × 6 factorial design feeding trial was conducted with three water temperatures (19°C, 23°C, and 27°C) and six protein levels (152.5, 202.5, 252.6, 302.6, 352.7, and 402.7 g/kg) for 90 days. Dietary protein levels and temperature significantly affected the growth performance of the hybrid abalones, but there was no interaction effect except for daily increment in shell length. Body moisture decreased with increasing water temperature, and crude protein showed a contrary tendency. Crude lipid and ash were not affected by dietary protein level or water temperature. The alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase activities and the triglyceride content in serum increased with increasing water temperature, whereas the opposite was true for albumin activity and total protein and glucose contents. Total cholesterol contents decreased with increasing dietary protein levels. Dietary protein levels and water temperature did not affect contents of high-density lipoprotein cholesterol and low-density lipoprotein cholesterol ( P &gt; 0.05 ). A significant interaction was observed between dietary protein levels and water temperature in all antioxidation parameters (reactive oxygen species, total antioxidant capacity, protein carbonyl, superoxide dismutase, catalase, glutathione s-transferase, and glutathione peroxidase except for malondialdehyde content). Based on specific growth rate, the optimal dietary protein levels for juvenile hybrid abalones were 333.1, 318.6, and 306.3 g protein/kg diet at 19°C, 23°C, and 27°C, respectively. These findings will help to develop multidiet feeding strategies at different water temperatures throughout the culture period of juvenile hybrid abalones.

Dietary Crude Protein Levels Alter Diarrhea Incidence, Immunity, and Intestinal Barrier Function of Huanjiang Mini-Pigs During Different Growth Stages.

Huanjiang mini-pig is an indigenous pig breed in China; however, the optimal dietary crude protein (CP) levels for this pig breed during different growth stages has not been standardized yet. This study investigated the effects of different CP levels on diarrhea incidence, immunity, and intestinal barrier function in pigs. A total of 360 Huanjiang mini-pigs were assigned to three independent trials and fed the following CP diets: 5−10 kg stage, 14, 16, 18, 20, and 22%; 10−20 kg stage, 12, 14, 16, 18, and 20% and 20−30 kg stage, 10, 12, 14, 16, and 18%. In the 5−10 kg stage, the 22%; diet increased the plasma IL-1β, IL-6, IL-8, and TNF-α concentrations compared to the 14−20% diets and decreased IL-10 and TGF-β; however, these results were fluctuated in the later stages, including the decrease of IL-1β and IL-8 in the 20% group, TNF-α in the 18−20% groups, and the increase of IFN-γ in the 20% group at the 10−20 kg stage and the decrease of TNF-α in the 16% group at the 20−30 kg stage. The 20% diet increased the jejunal and ileal IL-10 concentration compared to the 14% diet at the 5−10 kg stage, as well as in the 16% diet compared to the 12% diet at the 10−20 kg stage. In addition, ileal IL-10 concentration was increased in the 16% diet compared to the 10, 12, and 18% diets at the 20−30 kg stage. Furthermore, the 18% diet at the 5−10 kg stage and the 16% diet at the 10−20 kg stage decreased jejunal IL-6 expression, whereas the 20% diet increased the TNF-α and IFN-γ at the 5−10 kg stage. The 20% diet increased the Claudin, Occludin, ZO-1, ZO-2, Mucin-1, and Mucin-20 expressions at the 5−10 kg stage, as well as TLR-2, TLR-4, and NF-κB in the 22 and 20% diets at the 5−10 and 10−20 kg stages, respectively. Collectively, these findings suggest optimal dietary CP levels of 16, 14, and 12% for Huanjiang mini-pigs during the 5−10, 10−20, and 20−30 kg growth stages, respectively; and provide the guiding significance of dietary CP levels for Huanjiang mini-pigs during different growth stages.

Dietary lipid and protein levels influence the growth and feed utilisation of large yellowtail kingfish (Seriola lalandi) at summer water temperatures

Yellowtail Kingfish (Seriola lalandi; YTK) have a fast growth rate, and as a result, a high energy demand that could be satisfied by dietary lipids. The aim of this experiment was to determine the optimum dietary protein and lipid levels for large YTK maintained during a summer growing season. In this 84-day experiment (2 × 3 factorial design), the growth, feed utilisation and health of YTK (initial weight 2.13 ± 0.02 kg, mean ± SE) fed two nominal lipid levels 25% crude lipid (CL) (20 MJ kg−1 energy) and 30% CL (21 MJ kg−1 energy) and three nominal crude protein (CP) levels (40, 44 and 48%) were investigated. The specific growth rate of fish was significantly affected by the interaction between dietary CP and CL level. The results indicate that fish fed the 25% CL diets grew better than those fed the 30% CL diets. The interaction effect was primarily driven by the significant increase in growth for fish fed diet 1 (40% CP × 25% CL) and diet 2 (44% CP × 25% CL) compared to their respective 30% CL diets, diet 4 (40% CP × 30% CL) and diet 5 (44% CP × 30% CL). The growth of fish fed diet 3 (48% CP × 25% CL) and diet 6 (48% CP× 30% CL) was not significantly different. Feed conversion ratio (FCR) was not significantly influenced by diet however, the fish fed the 25% CL diet series and 40% protein series consumed the most feed. Fish fed the 25% CL series increased their feed intake with decreasing dietary CP level, to potentially compensate for reduced dietary protein. In contrast, fish fed the 30% CL series did not. Crude protein intake was higher when fish were fed the 48% CP diets and was reduced when fed the 40% and 44% CP diets. This response was more pronounced in the 30% CL diet series. There were no negative health effects noted during the study for various analyses including blood biochemistry and haematology, and gastrointestinal tract morphology. Numerically, the highest final weight, biomass gain, SGR, and FCR were consistently observed in the fish fed diet 2, however these were not significantly different to diet 1. Based on the combined results for 2.1–3.5 kg YTK raised during summer, the diet should contain at least 42.9% CP and 25.3% CL (equivalent to diet 2) corresponding to 19.9 MJ kg−1 GE diet with and a CP: GE ratio of 21.6 g MJ−1. In terms of actual protein and energy intake required this corresponds to 5.2 g CP−1 kg BW−1 d−1 (4.5 g DP−1 kg BW−1 d−1) and 242 KJ−1 GE kg BW−1 d−1 (207 KJ−1 DE kg BW−1 d−1) which appears to be optimal. We do not recommend diet lipid levels of approximately 30% over summer periods, as demonstrated in this experiment.

Optimal dietary protein level for pacu Piaractus mesopotamicus juveniles reared in biofloc system

This study evaluated the effects of dietary protein levels on growth performance, hematological and biochemical parameters, carcass and fillet yields, somatic indexes, and body chemical composition of pacu juveniles reared in a biofloc system over a 60-day period. Five isoenergetic (13.4 MJ kg−1 DE) experimental diets were formulated with increasing crude protein (CP) levels (194, 232, 278, 316, and 359 g kg−1). Three hundred fish weighing an average of 3.16 ± 0.3 g were randomly distributed in 20 experimental tanks (50 L) at the rate of 15 fish per replicate and fed experimental diets until apparent satiation four times a day. The experimental design was completely randomized with five treatments and four replicates. Weight gain (WG), thermal growth coefficient (TGC), protein productive value (PPV), and fillet yield (FY) showed quadratic effect (P < 0.05) as protein levels increased. Feed consumption (FC) and carcass yield (CY) showed a linear growth (P < 0.05), while protein efficiency ratio (PER) decreased linearly (P < 0.05) as protein levels increased. The hematological and biochemical parameters did not differ between treatments (P > 0.05), except for the hematocrit. However, blood parameters remained at normal range for this species. The optimal dietary protein level was estimated at 310 g kg−1 CP (≈ 268 g kg−1 DP) for the best growth of pacu juveniles reared in the biofloc system.

Effects of dietary protein level on the growth, reproductive performance, and larval quality of female yellow catfish (Pelteobagrus fulvidraco) broodstock

This study was conducted to evaluate the effects of dietary protein levels on the growth, spawning, and larval quality of female yellow catfish (Pelteobagrus fulvidraco) broodstock through a six-week feeding trial. Five isoenergetic diets were formulated, and the crude protein levels were 34.4 (DP34), 38.8 (DP39), 44.2 (DP44), 49.3 (DP49), and 52.7% (DP53). The results showed that the growth and reproductive performance, including the specific growth rate (SGR), feed efficiency (FE), gonadosomatic index (GSI), and hatching rate of yellow catfish broodstock in the DP44, DP49, and DP53 groups were significantly higher than those of other groups (P < 0.05). The optimal dietary protein levels for yellow catfish broodstock were 45.8% and 44.1% based on SGR and GSI. The lowest condition factor (CF), GSI, and smallest egg size were found in the DP34 group, while the total egg production was the highest in the DP53 group. Vitellogenin (VTG) contents in eggs and plasma were enhanced significantly with the increasing dietary protein levels from 34% to 49%, but decreased precipitously in the DP53 group (P < 0.05). The optical densities of androgen receptor (AR) and estrogen receptor (ER) in the DP34 group were significantly lower than those in other groups. The mRNA expression levels of CYP19a, AR, and ERβ were significantly increased in the DP49 group (P < 0.05). For larval quality, the deformity rate decreased significantly with the increasing dietary protein levels (P < 0.05). The larval survival rate at 9 DPH (days post-hatching) as a function of dietary protein level was analyzed by second-order polynomial regression. The results showed that a level of 47.7% was optimal for improving larval quality. Thus, a suitable range of dietary protein of yellow catfish broodstock for growth and reproduction is 44.1–47.7%.

Effects of dietary protein levels on the growth, digestive enzyme activity and fecundity in the oriental river prawn, Macrobrachium nipponense

The effects of dietary different protein levels on growth performance, body composition, digestive enzyme activity and fecundity were tested in the oriental river prawn Macrobrachium nipponense. Five iso-energetic and iso-lipidic experimental diets were formulated with graded levels of protein [31.34% (A), 33.87% (B), 36.95% (C), 39.56% (D) and 42.58% (E)]. The results showed that M. nipponense fed diets with 39.56% protein level exhibited the best growth performance, survival, feed conversion rate and protein retention. Following the measurement of digestive enzyme activity in treatment D showed significantly improved (p < 0.05) hepatopancreatic amylase and protease activities compared with treatments A and B. Interestingly, dietary protein levels significantly affected the basal composition of eggs. Furthermore, the dietary protein levels of 36.95% and 39.56% showed significantly higher total protein and lipid content in eggs than the control (31.34%). According to the results of berried females, reduced spawning frequency towards the end of the feeding trial period was observed. Broken-line regression analysis indicated that the optimal dietary protein levels for egg quality are 37% (% dry matter) for juvenile Macrobrachium nipponense.

Effects of dietary protein on water quality, growth performance, RNA/DNA ratio and haemato-immunological indices of soft-shelled turtle (Pelodiscus sinensis)

In aquatic animals, dietary protein plays a crucial role in their growth and immunity. A feeding trial was conducted on soft-shelled turtles (Pelodiscus sinensis) to assess the effects of various levels of protein on the specific growth rate (SGR), ambient water quality (total ammonia nitrogen (TAN), total nitrogen (TN) and total phosphorus (TP)), hematological parameters (respiratory burst (RB), red blood cell count (RBC), albumin content (Alb), hemoglobin level (Hb) and osmolality), plasma immunoglobulin M (IgM) levels and lysozyme activity. Soft-shelled turtles weighing about 4.02 g were fed fish meal-based diets with 14.38%, 20.41%, 26.19%, 32.23%, 37.63% and 45.23% protein for 8 weeks. SGR, RBC, Hb, Alb, RB, IgM and lysozyme activity were enhanced as the dietary protein was increased from 14.38% to 26.19%, then reached a plateau. For identical feeding times, TAN and TN were increased with elevating dietary protein levels. While, no statistically significant differences were observed among the 26.19%, 32.23% and 37.63% groups. When the turtles were cultivated for 56 days and fed with 45.23% protein, the TP in the culturing water was higher than that in the other groups. An increase in dietary protein level up to 26.19% increased the RNA/DNA ratio, which subsequently plateaued at a steady level. The levels of dietary protein had no impact on osmolality or alkaline phosphatase (AKP) activity. On the basis of broken-line analyses derived from SGR, the optimum dietary protein level for soft-shelled turtles was found to be 27.11% protein.

Impact of dietary protein levels on growth, feed utilization, body composition, and hematological characteristics of juvenile hybrid pufferfish (Takifugu obscurus × T. rubripes)

In the present study, we aimed to evaluate the optimum dietary protein level in hybrid pufferfish (Takifugu obscurus ♀ × T. rubripes ♂). To this end, we formulated five isoenergetic (16 MJ/kg gross energy) diets with casein with different levels of protein–namely, 35%, 45%, 50%, 55% and 65%. Then, fish with the average weight of 5.68 ± 0.05 g (mean ± SD) were randomly distributed into 15 tanks, 20 animals in each tank. The fish received their diet twice a day (09:00 and 17:00) ad libitum. The results showed that, after the 8-weeks feeding trial, the fish that received 45% and 50% protein diets had significantly higher final weight, WG, and SGR that the fish that received 35% protein diet (p < 0.05). However, final weight, WG and SGR did not differ significantly among the fish that received 35%, 55% and 65% protein diets. Next, the fish on 35% protein diet had a significantly higher PER that their counterparts on 50%, 55% and 65% protein diets (p < 0.05). However, no such difference was observed between the two groups of fish that received 35% and 45% protein diets. Furthermore, the fish on 50% and 55% protein diets had a significantly higher whole body protein content as compared to the fish that received 35% and 65% protein diets (p < 0.05). In addition, the fish on 65% protein diet had a significantly higher whole body lipid content as compared to the group that received 35% protein diet (p < 0.05). In addition, the highest arginine, histidine, phenylalanine, threonine, valine, glutamic acid, proline and tyrosine content were observed in the fish that received 50% protein diet. The fish on 35% and 65% protein diets had a significantly higher hemoglobin than the group on 55% protein diet (p < 0.05); however, no differences were observed among the groups on 45%, 50%, and 55% protein diets. Finally, the fish fed 35% has a significantly higher AST activity that the groups that received 45% and 55% protein diets (p < 0.05); yet, no significant differences were found among the groups on 45%, 50%, and 55% protein diets. The results of two-slope straight broken-line and quadratic broken-line analysis of WG revealed that, for the maximum growth of juvenile hybrid pufferfish, the optimal dietary protein should be 46.3% and 51.5%, respectively.

Effects of Different Dietary Protein Levels on the Growth Performance, Serum Biochemical Parameters, Fecal Nitrogen, and Carcass Traits of Huanjiang Mini-Pigs.

The Huanjiang mini-pig is a Chinese local breed and, the optimal dietary crude protein (CP) level for this breed is still unknown. Therefore, the present study was conducted to investigate its optimum dietary CP level upon the growth performance, serum biochemical parameters, fecal nitrogen content, and carcass traits. Three independent trials with 360 pigs were included. A total of 220 pigs (5.32 ± 0.46 kg) were fed ad libitum, either a 14, 16, 18, 20, or 22% CP diet from about 5- to 10-kg (trial 1); 84 pigs (11.27 ± 1.43 kg) were fed either a 12, 14, 16, 18, or 20% CP diet from about 10- to 20-kg (trial 2); and 56 pigs (18.80 ± 2.21 kg) were fed either a 10, 12, 14, 16, or 18% CP diet from about 20- to 30-kg (trial 3). In trial 1, as dietary CP levels increased, the feed-to-gain ratio (F/G) quadratically decreased (p < 0.05) and was minimal at the 18.42% CP level. The average daily feed intake (ADFI) and final body weight (BW) were not affected by dietary CP levels while the fat percentage decreased (p < 0.05). Besides, a linear decrease in slaughter rate (p = 0.06) and a linear increase in bone percentage (p < 0.05), serum urea nitrogen (UN) (P < 0.05), and fecal nitrogen content (p = 0.07) of pigs were observed. In trial 2, as dietary CP levels increased, the average daily gain quadratically increased (p < 0.05) and was maximum at the 16.70% CP level. The slaughter rate linearly decreased (p < 0.05) whereas the skin rate, serum UN, and NH3-N increased (p < 0.05) linearly, as well as fecal nitrogen content (p = 0.06). In trial 3, as dietary CP levels increased, the F/G increased (p < 0.05), while the ADFI and ADG quadratically decreased (p < 0.05) and was maximum at nearly 14.00% CP level. The bone percentage and serum UN increased (p < 0.05) linearly but the slaughter rate decreased (P < 0.05) linearly, and the fecal nitrogen content quadratically decreased (p = 0.07) whereas the albumin increased (p < 0.05) quadratically. Taken together, the optimal dietary CP levels for growth performance of Huanjiang mini-pigs from 5- to 10-kg, 10- to 20-kg, and 20- to 30-kg were 18.42, 16.70, and 14.00%, respectively.